It works in Workspaces but not in the challenge, what am I doing wrong?

# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.
def num_teachers(teachers):
    return len(teachers)


def num_courses(courses):
    total_courses = 0
    for teacher in courses.values():
        for course in teacher:
            total_courses += 1
    return total_courses


def courses(arguments):
    allcourses = []
    for courses in arguments.values():
        allcourses.extend(courses)
    return allcourses


def most_courses(courses):
    totalcourses = 0
    instructor = ""
    for teacher in teachers:
        courses = len(teachers[teacher])
        if  courses > totalcourses:
            max_courses = len(teachers[teacher])
            instructor = teacher
    return instructor